1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a system and method of detecting and preventing fraudulent long distance telephone calls in a radio telecommunication system.
2. Description of Related Art
In existing radio telecommunications networks, fraudulent users may attempt to place free long distance telephone calls by causing the network to recognize the calls as being placed by a legitimate subscriber. Fraudulent users may clone the legitimate subscriber's mobile telephone, including the electronic serial number (ESN) and mobile identification number (MIN). Thereafter, the cloned telephone appears to the network to be the subscriber's legitimate telephone, thereby allowing a fraudulent user to place illegitimate long distance telephone calls.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 4,955,049 to Ghisler discusses subject matter that bears some relation to matters discussed herein. Ghisler discloses a method of supervising subscribers in a mobile telephone system to detect fraudulent usage of a mobile telephone. Ghisler assigns a predetermined sequence of numbers to each mobile telephone in the system. Each time a call is made by a subscriber, the next number in the mobile telephone's assigned sequence is transmitted by the mobile station to the serving mobile switching center (MSC). The MSC records the numbers utilized, and detects a fraudulent call if there is a break in the sequence.
Ghisler, however, requires modification of each mobile station to store its assigned number sequence and transmit the next number in the sequence each time a call is made. It would be advantageous to have a method of detecting fraudulent telephone calls that does not require modification of the mobile station.
U.S. Pat. No. 5,309,501 to Kozik et al. (Kozik) discloses a modular switching system for detecting fraudulently identified mobile stations in a cellular mobile telecommunications network. Kozik is a switch-based fraud-detection system which examines a class of state transitions to see if a particular mobile station state transition is likely, in view of a recorded prior state of the mobile station. Unlikely state transitions are indications of possible fraud. Kozik, however, only works if the legitimate mobile station and the fraudulent mobile station are in the same location. The fraud detection algorithm utilized in Kozik assumes that there are two mobile stations in the same location, and finds an indication of fraud if both of the mobile stations are doing the same thing (i.e., going through the same state transition) in the same location.
A major disadvantage to the system and method of Kozik is that fraudulent mobile stations are often not in the same location as the legitimate mobile station. The switch-based system and method of Kozik will not detect fraudulent mobile stations operating in locations different from the legitimate mobile station, especially in the coverage area of another switch. Therefore, a system and method are needed that detects fraudulent mobile stations operating in locations different from the legitimate mobile station, and in the coverage area of different switches.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of detecting fraudulent telephone calls in a radio telecommunications network that does not require modification of the mobile station, and that detects fraudulent mobile stations operating in locations different from the legitimate mobile station, and in the coverage area of different switches. The present invention provides such a method.